A method for enhancing the efficiency of energy transfer from a relativistic electron beam to an electromagnetic wave in a Cherenkov laser is proposed. In a two‐dimensional Cherenkov laser composed of a planar relativistic electron beam and a parallel plate waveguide loaded with a dielectricgrating, either one of the grating parameters, or the slot width and the groove depth, is tapered or gradually decreased in accordance with the decrease in the drift velocity of the electron beam. The numerical simulation demonstrates that sufficient efficiency enhancement can be achieved by a tapered dielectricgrating.

In this letter, we report a quantum well infrared photodetectorgeometry for normal incidence light coupling. The new optical coupling scheme utilizes total internal reflection at the sidewalls of triangular wires to create favorable optical polarization for infrared absorption. These wires are created by chemically etching an array of V grooves through the detector active region along a specific crystallographic direction. Experimental results from the initial single color as well as two‐color detectors with linear wires and unthinned substrate show efficient light coupling comparable to the standard 45° edge coupling, without the undesirable wavelength dependence or spectral narrowing effect of a conventional grating structure. At the same time, the dark current density is substantially reduced due to the partial material removal. Further improvement is expected by creating a two‐dimensional coupling structure with substrate thinning.

We demonstrate a novel approach to phase insensitive, all‐optical steering and switching based on an intensity‐induced change in the propagation direction of multidimensional spatial solitary waves in bulk, birefringent, quadratic nonlinear media. Our demonstration is based on second‐harmonic generation in a KTP crystal. Compensation for the lateral displacements due to walkoff in SHG is observed.

Performance requirements for systems employing optical guided wave components may be satisfied more easily through the hybrid integration of nonlinear optical (NLO) polymers and semiconductors. Reported in this letter, is the integration of NLO polymer waveguides with InGaAsp‐i‐n photodetectors at 1.3 μm, with coupling efficiencies greater than 99% and system responsivities of 0.84 A/W. An analysis of the structure using a two‐dimensional beam propagation model was performed. Planarization was maintained and the design allows for further integration of optoelectronic components.

A mixed‐mode twisted nematic (MTN) liquid crystal cell is developed for both reflective‐mode projection and direct‐view displays. This MTN cell exhibits two times higher brightness and eliminates the parallax problem as commonly observed in reflective displays using a nominal transmissive TN cell. In the meantime, the MTN structure preserves advantageous characteristics of the TN structure such as low operation voltage and high contrast ratio. Confirming computer simulations using Jones matrix method agree with the experimental results well.

Fine structure has been observed in the 1.4 eV luminescence band of thin (≊100 Å) amorphous silicon (a‐Si:H) layers deposited on silicon substrates. The energy separation between the peaks is ≊20 meV. A similar luminescence band observed in layers grown on glass substrates under the same conditions is several orders of magnitude lower in intensity and is without perceptible fine structure. There is no change in the nature of the fine structure and the peak energies in filmsdeposited at different substrate temperatures (150–300 °C). The dependence of the luminescence band on illumination intensity and on temperature has also been measured. This indicates probable excitonic nature of the luminescence. Possible causes for the observed phenomena are discussed.

The critical splay‐to‐bend‐alignment transition in a liquid‐crystal cell treated by parallel rubbing (π cell) was investigated to improve the optical performance of the display mode using this cell with a compensator. By analyzing the free energy in liquid crystal cells, it was found that nematic media with a smaller K33/K11 ratio can reduce the transition voltage considerably, and therefore, also reduce the required optical anisotropy of the liquid‐crystal cell. The significantly improved viewing angle for this mode, achieved by using these newly designed parameters, is also confirmed theoretically and experimentally.

A hybrid, optoelectronic sampling circuit based on a photoconductive switch and a junction‐field‐effect‐transistor (JFET) source follower/amplifier has been demonstrated to have picosecond response, high‐sensitivity, absolute‐voltage capability, and a very high impedance. The distributed capacitance of the electrical measurement system is reduced to the gate input capacitance of the JFET, and the conventional photoconductive currentmeasurement is transferred into an absolute voltage measurement. Gating measurements with an improvement of 150 times in output voltage over unamplified photoconductive gates have been made using only 10 μW of average optical power. The effective on‐state resistance of the photogate has also been increased by more than 150 times, indicating that a photoconductive probe with very low invasiveness may be produced.

We have grown Nd:MgO:LiNbO3 crystals with periodic ferroelectric domain structures.Absorption and fluorescence spectra measured on these crystals showed little difference from those from Nd:MgO:LibO3 with uniform domain structures. Green fluorescence was generated by self‐frequency doubling in a cavity having great losses and pumped by a pulsed dye laser.

The influence of annealedproton exchanged (APE) waveguides on domain inversion in Z‐cut LiNbO3 is reported. For this study, pyrophosphoric acid is used to fabricate planar APE waveguides, both before and after creating domain inversion through the application of an external electric field at room temperature. Domain inversion produced in this manner is shown to sustain the APE process. However, domain inversion is not producible in portions of the substrates having APE waveguides on both crystal faces. The implication of this result for integrated optic devicefabrication is discussed.

Insituelectrochemicalscanning tunneling microscopy(STM) was used to examine n‐type GaAs(001), (111)A, and (111)B surfaces in 0.05 M sulfuric acid. Cathodic polarization of the GaAselectrodes effectively inhibited the oxidation of the surface, making it possible to acquire STM images with atomic resolution. Atomically‐flat terrace‐step structures were consistently observed on all surfaces prepared by the chemical etching method. Steps observed on these surfaces are composed of double layers with step heights of 0.28 and 0.33 nm for the (001) and (111) surfaces, respectively. InsituSTM atomic images revealed that those surfaces have (1×1) structures with the square and hexagonal lattices, respectively.

A large‐diameter uniform electron cyclotron resonanceplasma is produced by using multiannular antenna which has a capability of adjusting the radiated powers from two annular slits driven by two microwave sources. The radial profile of the ion saturation current can be varied from hollow to hill‐type shape by controlling radial profile of radiated microwave power of the multiannular antenna. In optimum conditions, the plasma has ±2.9% uniformity over 280 mm in diameter with electron density of 6×1010 cm−3. This plasma source is applied to a‐Si:H deposition and c‐Si etching. It is shown that the radial profile of the deposition rate as well as that of the etching rate can be controlled by changing the radial power radiation profile.

Time‐ and/or space‐resolved spectra of laser‐produced Al plasmas were investigated using a framing crystal x‐ray spectrometer. Population inversion was directly observed between the n=4 and n=3 levels in He‐like Al, and the correspondent numerical simulation well describes observed characteristics. Plasma evolution and their effects on inversion was shown on a Te–Ne map, and discussions on the optimum conditions based on the experiments and calculations are also given.

The infrared Raman spectrum of chemical vapor deposited(CVD)diamondfilms has been correlated with the in‐plane thermal conductivity of the films. The scattering strength of the 1332 cm−1 zone‐center phonon line of diamond, measured relative to the intensity of the nondiamond carbon phase, was found to increase strongly with increasing thermal conductivity. A good correlation between these two properties was found even for the highest quality CVDdiamondfilms with peak thermal conductivities up to 54 W/cm K. The dependence of the peak thermal conductivity on the intensity of the 1332 cm−1phonon line normalized to the scattering strength of the nondiamond carbon phase can be described by a power law with an exponent of 0.5.

We utilized a miniature sputtering cell with mylar windows and multitarget sputtering guns in order to study the growth of YBCO/LaAlO3superlattices on SrTiO3 substrates. Computer modeling of the diffraction spectra enabled us to determine the interface width between the layers. After deposition of the superlattices, the substrate temperature was increased to study any interdiffusion.

Potassiumniobate (KNbO3) thin films and potassium niobate/tantalate (KNbO3/KTaO3) superlattices have been grown on KTaO3 (001) substrates by pulsed laser deposition. The thin‐film structures were analyzed by Rutherford backscattering/ion‐channeling techniques, x‐ray θ–2θ and Φ scans, and both conventional and Z‐contrast scanning transmission electron microscopy. Excellent film flatness and crystallinity are evidenced by these techniques. At room temperature, the KNbO3films are characterized by an orthorhombic structure which differs from that of bulk KNbO3. The interfaces between the layers in the KNbO3/KTaO3superlatticestructures were found to be compositionally sharp on an atomic scale.

Highly oriented diamondfilms with {001} facets were grown on Si{001} using microwaveplasma enhanced chemical vapor deposition. The tilt and rotation of the diamond crystals were measured by polar x‐ray diffraction. The full widths at half‐maximum of {004} and {220} diffraction peaks were 5° and 10°, respectively. It was found that the {220} diffraction poles split into two peaks by approximately 5°. This result indicated that there were two possible azimuthal rotations about the surface normal of the substrate for the epitaxially nucleated diamond grains.

At a high temperature of about 1500 K, the migration of a Si microcluster was observed on a Si(001) surface by using an electron microscope. This cluster always existed together with an attendant region. This region melted first during heating because of its lower crystallinity compared to the Si substrate. The Si atoms in this melted zone were struck by electrons moving towards the anode and were pushed by the electron wind in the same direction as the electrons. The Si microcluster floating in the melted zone also migrated toward the anode side about ten times as fast as the Si electromigration atoms moving in the opposite direction.

We have succeeded in the fabrication of a boron–carbide/boron diode on an aluminum substrate, and a boron–carbide/boron junction field effect transistor. Our results suggest that with respect to the approximately 2 eV band gap pure boron material, 0.9 eV band gap boron–carbide (B5C) acts as a p‐type material. Both boron and boron–carbide (B5C) thin films were fabricated from single source borane cage molecules using plasma enhanced chemical vapor deposition (PECVD). Epitaxialgrowth does not appear to be a requirement.

100 ppm PH3 diluted in hydrogen is used as the n‐type dopant gas in Si and Si1−xGex epilayers grown by ultrahigh vacuum chemical vapor deposition (UHVCVD) using Si2H6 and GeH4. The phosphorus concentration in Si increases linearly at a small PH3 flow rate and becomes nearly saturated at higher flow rates, while the phosphorus concentration in Si1−xGex only shows a nearly linear behavior with PH3 flow rate. The growth rates of Si and Si1−xGex epilayers decrease seriously (∼50%) and slightly (∼10%) with the increase of PH3 flow rate, respectively. These results can be explained by a model based on the enhancement of hydrogen desorption rate at smaller PH3 flow rates and different levels of the effects of phosphorus blocking of surface‐activated sites between Si and Si1−xGex epilayers at higher PH3 flow rates.